使用jsp从数据库中删除行

Question

问题在于，当我点击deletedata-out.println(value)中的userNotes.jsp测试函数中的DELETE按钮时，它会起作用--它会向我显示在按钮上点击的内容的当前值，而不会显示其他内容。它不会从数据库中删除数据，也不会在响应时发送重定向，我需要做什么？
userNotes.jsp

                        <table id="notes" border="2">
                            <tr>

                                <td>note name</td>
                                <td>note</td>

                            </tr>
                            <%
                                PrintWriter writer = response.getWriter();
                                int id = Integer.parseInt(request.getParameter("r"));
                                try {
                                    Class.forName("com.mysql.jdbc.Driver");
                                    Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/evernoteDB",
                                            "evernoteDB", "0633739768z");

                                    Statement st = con.createStatement();
                                    ResultSet rs;
                                    rs = st.executeQuery("SELECT * FROM note");

                                    while (rs.next())
                                    {
                            %>
                            <tr>
                                <td><%=rs.getString(1) %></td>
                                <td><%=rs.getString(2) %></td>
                                <td>

                                            <a href=deleteData?id=<%=rs.getString(1) %>> Delete </a>

                                </td>
                       </tr>
                            <%

                                    }
                                    rs.close();
                                    st.close();
                                    con.close();
                                }
                                catch(ClassNotFoundException e)
                                {
                                    writer.println("Couldn't load database driver: " + e.getMessage());
                                }
                                catch(SQLException e)
                                {
                                    writer.println("SQLException caught: " + e.getMessage());
                                }
                                catch (Exception e)
                                {
                                    writer.println(e);
                                }

                            %>
                        </table>

deletedata-servlet

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.*;
import java.sql.*;


@WebServlet("/deleteData")
public class deleteData extends HttpServlet {

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    response.setContentType("text/html");
    PrintWriter out = response.getWriter();


    String value = request.getParameter("id");
    try {
        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/evernoteDB",
                "evernoteDB", "0633739768z");


        Statement st = conn.createStatement();

        st.executeUpdate("DELETE FROM note WHERE noteName=" + value);
        out.print(value);
            response.sendRedirect("http://localhost:8080/userNotes.jsp");

        conn.close();
    }
    catch(Exception e){
        e.printStackTrace();
    }
  }
}

Answer 1

列Notename的类型为string，因此执行查询应该引用该值。

st.executeUpdate("DELETE FROM note WHERE noteName='" + value + "'");

请考虑使用PreparedStatement。它很安全，也能处理此类错误。

既然您正在重定向，就不应该尝试设置任何内容标题。删除以下内容，因为servlet不应该写任何响应，而是要重定向。

response.setContentType("text/html");
PrintWriter out = response.getWriter();

另外，不要对主机和端口号进行硬编码，否则将无法在不同的服务器上部署生成的war。使用与sendredirect()类似的相对URL

conn.close();
response.sendRedirect("/userNotes.jsp");
return;